DESCRIPTION: (Applicant's Abstract) This is an hypothesis-driven case control study of human T-lymphotropic virus type II (HTLV-II) infection as a risk factor for pneumonia and skin and soft tissue abscess among injection drug users (IDU). It is well recognized that IDU have a high incidence of infectious diseases, including bacterial pneumonia and skin and soft tissue abscess. HTLV-II infection is prevalent among IDU at levels ranging from 5 to 15 percent in various United States cities. Recent data from our laboratory and from the multicenter Retrovirus Epidemiology Donor cohort study suggest that HTLV-II is associated with an increased prevalence of bacterial pneumonia, skin and soft tissue abscess, tuberculosis and other infections. We hypothesize that HTLV-II infection, because of mild immunosuppression, predisposes to infectious disease among IDU, who comprise the majority of HTLV-II infected subjects in this country. The proposed investigation includes two concurrent case-control studies among IDU at San Francisco General Hospital. IDU cases with diagnoses of 1) bacterial pneumonia; and 2) skin and soft tissue abscess (N=151 each) will be enrolled in parallel over three years from the in- and outpatient departments of San Francisco General Hospital. IDU without the above diseases, and matched to cases by age, race and in/outpatient status, will be enrolled concurrently into a single control group (N-302). HTLV-II infection, as determined by serology and polymerase chain reaction in our laboratory, will be the main risk factor measured in all subjects. Information on drug injection behavior (drug of choice, duration and frequency of drug injection, skin cleaning prior to injection) and intake of other drugs and alcohol will be obtained by interview to allow adjustment for confounding by these variables. HIV antibody will be measured as a possible confounding variable, and also to assess interaction with HTLV-II in predisposing to bacterial pneumonia and abscess. Finally, HTLV-II viral subtype by RFLP, and immunoglobulin G and CD4+/CD8+ lymphocyte levels will be measured in all subjects.